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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

FERRO-SILICON

195

FERRO-METALLIC   ALLOYS

Ferro-metallic alloys are forms of cast-iron, obtained in the blast furnace
or the electric furnace and containing, besides iron, larger or smaller pro-
portions of some special element. They are used for the preparation of
special steels (e.g., ferro-chromium, ferro-tungsten, etc.) or for the refining
of cast-iron or steel (e.g., ferro-silicon, ferro-aluminium, etc.). The quali-
tative investigation of the elements present is made as with special steels
(see p. 182).

FERRO-SILICON

This is generally prepared by fusion in the electric furnace of a mixture
of sand, coke and ferric oxide, and serves for the refining of cast-iron and
steel. The aim of the analysis is usually to establish the percentage of
silicon, but sometimes determinations are required of the impurities present,
e.g., carbon, manganese, phosphorus, sulphur, etc.

The types of ferro-silicon on the market nowadays are mostly of high
silicon content (more than 25-30%) and are therefore insoluble or incom-
pletely soluble in acids, so that they must be fused with alkali.

1. Determination of the Silicon.—Two methods are available:

(a] FUSION* WITH SODIUM CARBONATE AND PEROXIDE.* An intimate
mixture of 0-3-0-5 gram of the sample with 12-15 parts of sodium peroxide
(free from silica) and 6-7 parts of anhydrous sodium carbonate is heated
in a fairly large, covered nickel crucible, at first very carefully. When the
reaction begins to slacken, the temperature is gradually raised, the crucible
being heated round the walls rather than at the bottom, so that the mass
fuses quietly.

The cold crucible is treated in a dish with hot water, the crucible being
removed and washed and the solution, rendered distinctly acid with hydro-
chloric acid, evaporated to dryness in a porcelain dish. The residue is
heated in an oven at 135° to render the silica insoluble, the subsequent
procedure being as in the determination of silicon in iron. In this case,
however, it is necessary to evaporate to dryness the liquid from which the
silica has been removed by filtration and to heat the residue again at 135°
to recover the small quantity of silica always remaining in solution. In
the hydrochloric acid solution the manganese and phosphorus may be
determined (see p. 196). In this case also it is well to test the purity of the
silica obtained by treatment with hydrofluoric and sulphuric acids as on

P- 171-

(6) FUSION WITH SODIUM CARBONATE AND MAGNESIA. 0-3-1 gram of the
sample, very finely ground in an agate mortar, is mixed with about 10 parts
of an intimate mixture of sodium carbonate (2 parts) and magnesium oxide
(i part), the mixture being placed in a fairly large platinum crucible, the
bottom of which is covered with a thin layer of the sodium carbonate-

1 The accuracy of the method has been confirmed also by Namias : Ind. Chim,
Miner, e MetalL, 1915, II, p. 281.ating these elements in tungsten steels.